The present invention relates to combined potentiometer and switch units, and more particularly to such devices of the single-turn rotary type which are adaptable for use with a hearing aid.
Various hearing aid designs are presently available. For example, they may be encapsulated into an ear mold and inserted into or behind the wearer's ear, or mounted on a pair of eyeglasses. In either case, it is desirable that the hearing aid be as small as possible so as to minimize its weight and visibility. It is also important that the hearing aid control be adequately sealed. In addition to the normal atmospheric substances such as dust and moisture, the control must operate in an environment which includes perspiration, body oils, and the like. Adequate sealing is made difficult, however, due to the requirement that the control be manually adjustable and accordingly have a control knob or cap of appreciable size.
In addition to the potentiometer or variable resistance device for volume control, many hearing aid controls incorporate a switch to turn the device off when it is not in use and thus save wear on the battery. It is desirable that the switch have a snap feel when it is actuated so the user knows when the switch has been turned on or off. This snap feel should not, however, interfere with normal operation of the volume adjustment portion of the device, which should have a smooth rotational friction that gives the user a steady, positive feel as the volume is adjusted. In addition, it is of course always advantageous to reduce the complexity and cost of control devices, and to this end any parts that can be eliminated without impairing operation of the control is desirable.
In U.S. Pat. No. 3,518,604 to Beaver and Van Benthuysen an improved potentiometer sealing device is described. The potentiometer, which is not described as being intended for use with a hearing aid, includes a housing with an aperture through which a control driver is mounted. The driver comprises a body portion inside the housing and a cylindrical portion or barrel extending from the body portion outwardly through the aperture. The body portion is held firmly against the inner housing wall while the opposite end of the barrel is flared outwardly over the external edge of the aperture to form a flared bearing and dust-excluding seal around the periphery of the aperture. Although the patent notes the attainment of an adequate dust seal with the above construction, a preferred embodiment utilizes a lip, in the form of a flap around the periphery of the aperture, which is contacted by the barrel to improve the seal. A relieved area may underlie the flap so that a sufficient pressure of engagement between the flap and the flared bearing depresses the flap into the relieved area. While the described potentiometer may provide adequate sealing and torque control, further improvement is possible in terms of the complexity of both the component parts and the assembly procedure.